The present invention relates to a deployable divergent segment of a thruster comprising a stationary divergent portion and a movable divergent portion suitable for occupying a retracted position and a deployed position. More precisely, the invention relates to a system for deploying such a divergent segment and to a threaded rod forming part of such a system.
Such a threaded rod has a head suitable for being supported by a support secured to the stationary divergent portion and co-operating with rotary drive means for driving the threaded rod in rotation, and a tip suitable for being inserted in a holder sleeve secured to the stationary divergent portion, the threaded rod being suitable for co-operating with a nut secured to the movable divergent portion in such a manner that rotating said rod causes the movable divergent portion to move.
A control system of that type, and specifically having three threaded rods that are regularly spaced apart angularly, is disclosed in French patent application number 2944063. Overall, that system gives satisfaction, the threaded rods, also known as worm-screws, constitute both the elements that cause the movable divergent portion to move, and the means for guiding that movement. Nevertheless, the diverging segments of thrusters, and thus their deployment systems, are subjected to conditions that are extreme. In particular, in operation, ambient temperatures may be as high as 1600 K. As a result, the materials that can be selected for use are extremely restricted. In particular, the available materials are generally very sensitive to friction forces. When selecting a material, its ability to withstand very high temperatures needs to be given precedence over its tribological parameters.
Furthermore, as mentioned above, the threaded rod(s) of the system for deploying the divergent segment also contribute to guiding its movement. To do this, it is appropriate for the threaded rods to be held properly while they are rotating. Consequently, the clearance existing in the holder sleeve around the tip of the threaded rod is generally very small. This is also necessary for limiting vibration phenomena in operation. Nevertheless, because of the small size of this clearance, friction between the tip of the threaded rod and the inside surface of the sleeve in which it is inserted is large.
Furthermore, because of the environment of the divergent segment and because of the extreme conditions to which it is subjected in operation, the deployment system can become dirty, in particular in the region of the holder sleeve.
For all these reasons, there is a risk that the tip of the threaded rod might become jammed in the sleeve, during its rotation that is required for moving the movable divergent portion. Such jamming must be avoided in order to provide good operating conditions.